The present disclosure relates to the chloride process for the production of titanium dioxide pigment. This disclosure provides a route to a durable grade pigment, without the necessity of depositing surface treatments on the titanium dioxide particles by wet treatment.
Typically titanium dioxide particles may be produced by either the chloride or the sulfate process. In the chloride process, typically titanium dioxide is prepared by reacting titanium tetrachloride (TiCl4) with oxygen. This reaction occurs at temperatures of about 1200° C. to about 1600° C. The pigment properties of the so prepared titanium dioxide particles may then be modified to optimize the pigment properties of dispersion, optical spacing or durability by processing in one or more wet treatment operations to deposit metal oxides on the surface of the pigment. Deposits of aluminum oxide or combinations of aluminum oxide and silicon dioxide, used alone or in combination with other oxides, are typical constituents of commercial titanium dioxide pigment. Such surface treatments are deposited through precipitation of the desired metal oxide in a wet chemical reaction. Thus, the base pigment, that is, the titanium dioxide particles produced at the exit point of the oxidizer in the chloride process or after calcination in the sulfate process, must be washed and processed through one or more wet treatment steps. Wet treatment is then followed by washing, drying and grinding to produce a product suitable for use in for example, exterior coatings and plastics or paper products. The silicon dioxide added via wet chemistry requires additional grinding energy to obtain the desired finished product properties.
A process is needed that effectively coats titanium dioxide particles with silica to produce durable, non-yellowing substantially anatase-free titanium dioxide particles, having smaller particle size, while not requiring additional operating or equipment costs.